As the critical dimensions of integrated circuit patterns decrease with increasing integration densities, the resolution and depth of focus achieved during photolithography steps becomes more critical. Accordingly, highly planar semiconductor wafers are required. Planarization techniques have thus been developed to provide highly planar surfaces for semiconductor wafers. In particular, chemical-mechanical polishing systems and methods have been developed which provide simultaneous and efficient planarization for multiple wafers.
FIGS. 1 and 2 illustrate a conventional chemical-mechanical polishing (CMP) system. In particular, FIG. 1 is a plan view illustrating a conventional chemical-mechanical polishing system. FIG. 2A is a cross-sectional view taken along sections lines 2a--2a of FIG. 1, and FIG. 2B is a cross-sectional view taken along section lines 2b--2b of FIG. 1. As shown in FIG. 1, a polishing portion A is used to polish the surface of semiconductor substrates, and a cleaning portion B is used to clean the surfaces of the semiconductor substrates after polishing.
The polishing portion A of the system includes a first platen 10a having a flat end portion, a first platen rotating shaft 11a for rotating the first platen 10a, and a polishing pad 20a fixed on the end portion of the first platen 10a. The polishing portion also includes a conditioner 50 for cutting back a surface of the polishing pad 20 to expose a new surface thereof, a conditioning head 60 having an end portion fixed to the conditioner 50, and a conditioning head arm 61 for transferring the conditioning head 60. In addition, the clamp 40 has an end portion for fixing the semiconductor substrate 30 thereto, and a clamp arm 41 for transferring the clamp 40. Furthermore, the polishing pad 20a has fine grooves on its surface so that a polishing slurry can be provided to the center portions of the semiconductor substrate 30 even though maintained in tight contact with the polishing pad 20a.
The cleaning portion B includes a second platen 10b having a first end portion, a second platen rotating shift 11b for rotating the second platen 10b, and an auxiliary pad 20b fixed to the end portion of the second platen 10b. As shown, the clamp 40 to which the semiconductor substrate 30 is attached can be transferred from the polishing portion A to the cleaning portion B using the clamp arm 41.
The operation of the chemical-mechanical polishing system discussed above will now be explained with reference to FIGS. 1 and 2A-2B. The surface of the semiconductor substrate 30 is first polished by rotating the semiconductor substrate 30 in tight contact with the polishing pad 20a while a slurry is being deposited on the polishing pad 20a. The semiconductor substrate 30 is then moved away from the polishing pad 20a using the clamp 40 and the clamp arm 41. The surface of the polishing pad 20a is then cut back to expose a new surface thereof by rotating the conditioner 50 in tight contact with the polishing pad 20a. This operation is referred to as pad conditioning. The pad conditioning operation is used to reduce abrasion of the surface of the polishing pad 20a thereby maintaining the speed at which the semiconductor substrates 30 can be polished.
Stated in other words, the purpose for the pad conditioning operation is to expose a new polishing pad surface by cutting back the abraded surface of the polishing pad 20a. It may be difficult, however, to completely remove polishing particle lumps which may be formed by the agglutination of particles during the polishing step. Moreover, polishing particles from the slurry may also be difficult to remove. In particular, it may be very difficult to remove polished particle lumps and slurry particles jammed into grooves formed on the surface of the polishing pad 20a.
Accordingly, particle lumps remaining on the polishing pad 20a may produce scratches on the surfaces of semiconductor substrates polished thereon. In particular, polishing particle lumps may roughen the surface of semiconductor substrates 30 polished thereon thereby decreasing the reliability of the chemical-mechanical polishing operation. This result may occur because portions of the semiconductor substrate 30 exposed to the polished particle lumps may be more rapidly polished than portions not exposed to the lumps.
The polished semiconductor substrate 30 is then transferred from the polishing portion A to the cleaning portion B. The polish surface of the semiconductor substrate 30 is then cleaned by rotating the semiconductor substrate 30 in tight contact with the auxiliary pad 20b while depositing a cleaning solution onto the surface of the auxiliary pad 20b. Particles and polishing particle lumps, however, may stick to the semiconductor substrate 30 and may thus be transferred to the auxiliary pad 20b.
In addition to the cleaning operation discussed above, an auxiliary polishing operation can also be performed on the cleaning portion B of the chemical-mechanical polishing system. The auxiliary polishing operation can be used to remove scratches from the surface of the semiconductor substrate 30 formed during the polishing operation discussed above with reference to FIG. 2A. The auxiliary polishing operation is performed by depositing a slurry including polishing particles instead of the cleaning solution onto the auxiliary pad 20b. The auxiliary polishing operation is sometimes referred to as slurry buffing or touch up. Like the polishing operation, the auxiliary polishing operation may generate scratches on the surface of the semiconductor substrate 30 and roughen the surface of the semiconductor substrate 30.
Notwithstanding the methods and systems discussed above, there continues to exist a need in the art for improved chemical-mechanical polishing systems and methods.